@IanBish - Of course there is a danger in saying anything is normal, but this is certainly what you should expect to be happening from a purely metabolic perspective - with any insulin response like this (not using the "spike" term, nothing abnormal per se about the response) - you should expect to exit the "response" with a lower blood glucose level (and a higher insulin level) that when you started.
ie, carbs from the sourdough are piped into your liver, triggering pancreas to increase insulin. Insulin triggers tissue to take in more glucose, glucose level drops. When blood glucose gets low, pancreas stops producing insulin. The balance and timing of this all depends on exactly how sensitive you are with sourdough and insulin resistance.. This is really the trail of events that explains why snacking to "give you a boost" is often the opposite of what actually happens.. you end up with less energy.
Depending on you, personally, you may or may not benefit from that apple to "restore" your blood glucose, but it's likely (at least in my experience, which is quite old now) that you would see the same glucose raise back no normal background, as your insulin levels go back to normal. There is also the effect of stress that comes with looking at that red line appearing - just try to remember that low blood glucose in a T2 is not quite the same thing as low (and dropping) blood glucose in a T1. (though, I do totally get that feeling of being unwell and tired).
Alcohol is a whole other issue, with alcohol around, your liver must metabolise that before anything else.
4.9 is an excellent level by the way. Good work...
